For the timing chain or the like of the engine, a tensioner device has been heretofore extensively used in order to prevent a deflection when the chain runs. Tension is applied to the chain by a tensioner lever to take up the slack thereof.
FIGS. 6 and 7 show an example of a prior art tensioner device having a tensioner lever used for the timing chain of the engine. A chain 13 is stretched over a sprocket 10 on the driving side secured to a crank shaft of the engine and sprockets 11, 12 on the driven side at least one of which is secured to a cam shaft. Rotation of the crankshaft is transmitted from the drive sprocket 10 to the driven sprockets 11, 12 through the chain 13 whereby the cam shaft is rotatively driven. Between the drive sprocket 10 and the driven sprocket 12, the chain has a slack run. Between the driven sprocket 11 and the drive sprocket 10, the chain has a tension run.
A tensioner device 14 is arranged on the slack run of the chain 13 for taking up the slack to prevent the deflection during the running. The tensioner device 14 comprises a tensioner lever 16 supported pivotally about a pivot pin 15 so as to press against the slack run of the chain 13 to apply tension to the chain 13, and the device includes tensioner 18 having a plunger 17 for pressing the tensioner lever 16 against the chain 13.
As shown in FIG. 7, the tensioner lever 16 has a lever base 19 made of metal formed by bending a thick metal plate, and a shoe 20 made of resin is fixed in close contact with the surface of the lever base 19 confronting the chain 13. A proximal end portion 19A of the lever base 19 is shaped into a loop, into which is inserted a hollow cylindrical collar 21 made of metal pivotally fitted over the pivot pin 15. Further, the lever base 19 has a curved offset portion 19B locally curved on the side opposite to that confronting the chain 13 so that the extreme end of the plunger 17 shown in FIG. 6 comes in contact therewith. The overall shape of the lever base 19 is in an elongated arcuate shape in the form of a bow on the side confronting the chain 13.
On the other hand, a shoe 20 is secured to the lever base 19. The exposed side of a shoe surface 20A is in sliding contact with the chain 13. The shoe 20 is mounted in close contact with the surface of the metal plate 19 confronting the chain 13. In the curved offset portion 19B of the lever base 9, the shoe has a wall thickness which causes the exposed surface 20A to follow the arcuate shape of the plate 19, and a pad portion 20B whose surface confronting the plate surface conforms in contour to the contour of the curved portion 19B. The wall-thickness T between the exposed shoe surface 20A of that portion and the surface of the shoe confronting the lever base 19 on the side opposite thereof is considerably thicker than other portions. Further, the shoe 20 has a wall-thickness formed to be slightly thicker also in the periphery of the proximal end portion 19A of the lever base 19 bent along the outer peripheral surface of the metal collar 21 than other portions.
However, in the conventional shoe made of resin, in the portion which surrounds the periphery of the proximal end portion of the lever base to which are secured the pad portion and the metal collar, the thickness between the shoe surface and the surface in contact with the lever base on the back surface thereof is thicker than other portions. Therefore, when the shoe is subjected to molding, the flow of resin and the curing speed are not uniform, and may produce a distortion in the shape thereof, making it difficult to obtain a shape accurately adapted to the contour of the lever base. This poses a problem in that the shoe surface in sliding contact with the chain when assembled to the tensioner lever becomes inclined with respect to the pivotal surface of the tensioner lever which pivots about the pivot pin to produce a local abrasion on the shoe surface and to increase a friction between the shoe surface and the chain, resulting in a power loss.